RMS

Root mean square value of input or sequence of inputs

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Libraries:
DSP System Toolbox / Statistics

Description

The RMS block computes the root mean square (RMS) value of each row or column of the input, or along vectors of a specified dimension of the input. It can also compute the RMS value of the entire input. You can specify the dimension using the Find the RMS value over parameter. The RMS block can also track the RMS value in a sequence of inputs over a period of time. To track the RMS value in a sequence of inputs, select the Running RMS parameter.

Note

The Running mode in the RMS block will be removed in a future release. To compute the running RMS in Simulink^®, use the Moving RMS block instead.

Examples

Compute RMS of Noisy Step Signal

Use the RMS block to compute the RMS of a noisy square wave signal.

• Open Model

Ports

Input

In — Data input

vector | matrix | N-D array

The block accepts real-valued or complex-valued multichannel and multidimensional inputs.

This port is unnamed until you select the Running RMS parameter and set the Reset port parameter to any option other than None.

Data Types: single | double
Complex Number Support: Yes

Rst — Reset port

scalar

Specify the reset event that causes the block to reset the running RMS. The sample time of the Rst input must be a positive integer multiple of the input sample time.

Dependencies

To enable this port, select the Running RMS parameter and set the Reset port parameter to any option other than None.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Output

Port_1 — RMS value along the specified dimension

scalar | vector | matrix | N-D array

The data type of the output matches the data type of the input.

When you do not select the Running RMS parameter, the block computes the RMS value in each row or column of the input, or along vectors of a specified dimension of the input. It can also compute the RMS value of the entire input at each individual sample time. Each element in the output array y is the RMS value of the corresponding column, row, or entire input. The output array y depends on the setting of the Find the RMS value over parameter. Consider a three-dimensional input signal of size M-by-N-by-P. When you set Find the RMS value over to:

• Entire input — The output at each sample time is a scalar that contains the RMS value of the M-by-N-by-P input matrix.

• Each row — The output at each sample time consists of an M-by-1-by-P array, where each element contains the RMS value of each vector over the second dimension of the input. For an M-by-N matrix input, the output at each sample time is an M-by-1 column vector.

• Each column — The output at each sample time consists of a 1-by-N-by-P array, where each element contains the RMS value of each vector over the first dimension of the input. For an M-by-N matrix input, the output at each sample time is a 1-by-N row vector.

  In this mode, the block treats length-M unoriented vector inputs as M-by-1 column vectors.

• Specified dimension — The output at each sample time depends on the value of the Dimension parameter. If you set the Dimension to 1, the output is the same as when you select Each column. If you set the Dimension to 2, the output is the same as when you select Each row. If you set the Dimension to 3, the output at each sample time is an M-by-N matrix containing the RMS value of each vector over the third dimension of the input.

When you select Running RMS, the block tracks the RMS value of each channel in a time sequence of inputs. In this mode, you must also specify a value for the Input processing parameter.

• Elements as channels (sample based) — The block treats each element of the input as a separate channel. For a three-dimensional input signal of size M-by-N-by-P, the block outputs an M-by-N-by-P array. Each element y_ijk of the output contains the RMS value of the element u_ijk for all inputs since the last reset.

  When a reset event occurs, the running RMS y_ijk in the current frame is reset to the element u_ijk.

• Columns as channels (frame based) — The block treats each column of the input as a separate channel. This option does not support input signals with more than two dimensions. For a two-dimensional input signal of size M-by-N, the block outputs an M-by-N matrix. Each element y_ij of the output contains the RMS value of the elements in the jth column of all inputs since the last reset, up to and including the element u_ij of the current input.

  When a reset event occurs, the running RMS for each channel becomes the RMS value of all the samples in the current input frame, up to and including the current input sample.

Data Types: single | double

Parameters

Main Tab

Running RMS — Option to select running RMS

off (default) | on

When you select the Running RMS parameter, the block tracks the RMS value of each channel in a time sequence of inputs.

Find the RMS value over — Dimension over which the block computes the RMS value

Each column (default) | Entire input | Each row | Specified dimension

• Each column — The block outputs the RMS value over each column.

• Each row — The block outputs the RMS value over each row.

• Entire input — The block outputs the RMS value over the entire input.

• Specified dimension — The block outputs the RMS value over the dimension specified in the Dimension parameter.

Dependencies

To enable this parameter, clear the Running RMS parameter.

Dimension — Custom dimension

1 (default) | scalar

Specify the dimension (one-based value) of the input signal over which the RMS value is computed. The value of this parameter must be greater than 0 and less than the number of dimensions in the input signal.

Dependencies

To enable this parameter, set Find the RMS value over to Specified dimension.

Input processing — Method to process the input in running mode

Columns as channels (frame based) (default) | Elements as channels (sample based)

• Columns as channels (frame based) — The block treats each column of the input as a separate channel. This option does not support input signals with more than two dimensions. For a two-dimensional input signal of size M-by-N, the block outputs an M-by-N matrix. Each element y_ij of the output contains the RMS value of the elements in the jth column of all inputs since the last reset, up to and including the element u_ij of the current input.

  When a reset event occurs, the running RMS for each channel becomes the RMS value of all the samples in the current input frame, up to and including the current input sample.

• Elements as channels (sample based) — The block treats each element of the input as a separate channel. For a three-dimensional input signal of size M-by-N-by-P, the block outputs an M-by-N-by-P array. Each element y_ijk of the output contains the RMS value of the element u_ijk for all inputs since the last reset.

  When a reset event occurs, the running RMS y_ijk in the current frame is reset to the element u_ijk.

  Variable-Size Inputs

  When your inputs are of variable size, and you select the Running RMS parameter, then:

  • If you set the Input processing parameter to Elements as channels (sample based), the state is reset.

  • If you set the Input processing parameter to Columns as channels (frame based), then:

    • When the input size difference is in the number of channels (number of columns), the state is reset.

    • When the input size difference is in the length of channels (number of rows), there is no reset and the running operation is carried out as usual.

Dependencies

To enable this parameter, select the Running RMS parameter.

Reset port — Reset event

None (default) | Rising edge | Falling edge | Either edge | Non-zero sample

The block resets the running RMS whenever a reset event is detected at the optional Rst port. The reset sample time must be a positive integer multiple of the input sample time.

When a reset event occurs while the Input processing parameter is set to Elements as channels (sample based), the running RMS for each channel is initialized to the value in the corresponding channel of the current input. Similarly, when the Input processing parameter is set to Columns as channels (frame based), the running RMS for each channel becomes the RMS value of all the samples in the current input frame, up to and including the current input sample.

Use this parameter to specify the reset event.

• None — Disables the Rst port.

• Rising edge — Triggers a reset operation when the Rst input does one of the following:

  • Rises from a negative value to either a positive value or zero.

  • Rises from zero to a positive value, where the rise is not a continuation of a rise from a negative value to zero.

    

• Falling edge — Triggers a reset operation when the Rst input does one of the following:

  • Falls from a positive value to a negative value or zero.

  • Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to zero.

    

• Either edge — Triggers a reset operation when the Rst input is a Rising edge or Falling edge.

• Non-zero sample — Triggers a reset operation at each sample time, when the Rst input is not zero.

Note

When running simulations in the Simulink multitasking mode, reset signals have a one-sample latency. Therefore, when the block detects a reset event, there is a one-sample delay at the reset port rate before the block applies the reset. For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and Time-Based Scheduling and Code Generation (Simulink Coder).

Dependencies

To enable this parameter, select the Running RMS parameter.

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no

More About

Root Mean Square (RMS)

The RMS value of a discrete-time signal is the square root of the arithmetic mean of the squares of the signal sample values.

For an M-by-N input matrix u, the RMS value of the jth column of the input is given by:

$$y_j=\sqrt{\frac{{\displaystyle \sum _{i=1}^M{\left|u_{ij}\right|}^2}}{M}}1\le j\le N$$

Algorithms

Root Mean Square (RMS)

When you clear the Running RMS parameter in the block and specify a dimension, the block produces results identical to the MATLAB^® rms function, when it is called as y = rms(u,D).

• u is the data input.

• D is the dimension.

• y is the RMS value.

The RMS value along the entire input is identical to calling the rms function as y = rms(u(:)).

When inputs are complex, the block computes the RMS value of the magnitude of the complex input.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a